Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (18,019)	$ (9,414)	$ (35,186)	$ (17,533)
Other comprehensive income:
Unrealized gain on marketable securities	54	42	94	46
Total comprehensive loss	$ (17,965)	$ (9,372)	$ (35,092)	$ (17,487)